A cleaning process reduces the contamination risk in bone impaction grafting but also modifies the grain size distribution. The cleaned allograft shows a higher mechanical stability than the untreated group.

In revision total hip replacement, bone loss can be managed by impacting porous bone chips. The bone chips have to be compacted to guarantee sufficient mechanical strength. To improve the safety of bone grafts and to reduce the risk of bacterial and viral contamination, cleaning processes are used to remove the organic portion of the tissue while maintaining its mechanical characteristics.

A cleaning procedure described by Coraca-Huber et al. was compared to untreated allografts by performing a sieve analysis, followed by an uniaxial compression test. Differences in grain size distribution and weight loss during the cleaning procedure were compared to data from literature. Yield stress limits, flowability coefficients as well as initial density and density at the yield limit of the two groups were determined for each group over 30 measurements. The measurements were taken before and after compression with an impaction apparatus (dropped weight).

The cleaning process reduced the initial weight by 56%, which is comparable to the results of McKenna et. al. Cleaned allograft showed a 25% lower weight of bone chips sized > 4 mm compared to data from a previous study.

The cleaned bone chips showed a statistically significant (p > 0.01) higher yield limit to a compression force (0.165 ± 0.069 MPa) compared to untreated allograft after compaction (0.117 ± 0.062 MPa). The flowability coefficient was 0.024 for the cleaned allograft and 0.034 for the untreated allograft.

Initial density as well as the density at the yield limit was higher for the untreated allografts, as the sample weight was twice as high as in the cleaned group, to compensate for the washout of the organic portion. The cleaned bone grafts showed a higher compaction rate, which was 31%, compared the the untreated group with a compaction rate of 22%.

The cleaned allograft showed a higher compaction rate, which means that the gaps between the single grains are filled out with smaller particles, resulting in better interlocking. In the untreated allograft the interlocking mechanism is hindered by the organic elements. This observation is confirmed by a reduced flowabillity and a higher yield stress limit. The loss of weight as well as a higher compaction rate implies that more cleaned graft material is needed to fill bone defects in hip surgery. Sonication may damage the bone structure of the allograft and reduce the size of the particles.

Introduction: Total en bloc spondylectomy (TES) as the only radical treatment option for sarcoma and solitary metastases of the spine was shown to markedly minimize local recurrences, improve patient quality of life and substantially increase overall survival rates. Due to surgical difficulty of TES and complex biomechanical demands in defect reconstruction multisegmental tumor involvement of the spine has long been considered as a palliative situation, exceeding the limits of surgical feasibility. Thus, multilevel resections reports are very rare. For the first time, this study analyzes the onco-surgical results after multilevel thoracolumbar TES and reconstruction with a carbon composite vertebral body replacement system (CC-VBR) in a collective of patients.

Methods: 18 patients (9f/9m; age 52±14y) treated with thoracolumbar multilevel TES (6x2, 9x3, 3x4 segments) for spinal sarcomas (n=9), solitary metastases (n=5) and aggressive primary tumors (n=3) were retrospectively investigated. According to the classification system of Tomita et al. all patients were surgically staged as type 6 (multisegmental/extracompartimental). Defect reconstruction (11 thoracic, 3 thoracolumbar and 4 lumbar) were performed with posterior stabilization and a CC-VBR. Patient charts and the current clinical follow-up results were analyzed for histopathological tumor type, pre- and postoperative data (symptoms, duration of surgery, blood loss, complications, intensive care, adjuvant therapies etc.) and course of disease. Latest radiographs and CT-scans were analyzed at follow up. Oncological status was evaluated using cumulative disease specific and metastases-free survival analysis.

Results: With a mean follow up (100%) of 18 (4–44) months 17 patients (94%) were postoperatively ambulatory without any support. Postoperative neurological deficits were seen in one patient (6%). Wide resection margins were attained in 7, marginal in 11 patients. Depending on tumor biology/grading and/or resections margins an adjuvant therapy (radiation/chemotherapy) was performed in 12 (67%) patients. Local recurrence was found in one patient (6%). 13 (72%) patients showed no evidence of disease, 3 were alive with disease while 2 died of disease at 10 and 27 months postoperatively.

Conclusion: In selected patients with multisegmental spinal tumor involvement oncological sufficient resections can be reached by multilevel TES. Although the surgical procedure is challenging and the patient’s stress is considerable our encouraging midterm results together with the low complication rate clearly favour and legitimate this technique. However, treatment success strongly depends on adjuvant therapies. Reconstruction with a CC-VBR showed low complication rates, promising biomechanical characteristics, increased volume for bone grafting and lower artefact rates in follow-up MR- and CT-imaging.

Background Context: Total disc replacement (TDR) gained enormous popularity as a treatment option for symptomatic degenerative disc disease in the last few years. But the impact of the prosthesis design on the segmental biomechanics in most instances still remains unclear. As TDR results in a distraction of the capsuloligamentous structures, the disc height seems to be of crucial importance for the further biomechanical function of the operated level. Yet the biomechanical role of disc height after TDR still remains unclear.

Purpose: The purpose of study was to evaluate the influence of prosthesis height after total disc replacement on: 1) the sagittal balance and 2) the range of motion.

Study design: A radiological and an in-vitro biomechanical study.

Method: 6 human, lumbar spines L4–L5 were tested in vitro.The segmental lordosis of the specimen were measured on plain radiographs and the range of motion was measured for all six degrees of freedom with a previously described spine tester. The segmental lordosis and the range of motion at level L4–L5 was evaluated for following settings: 1) intact state 2) after implantation of a prosthesis with 5mm endplate 3) after implantation of a prosthesis with 7mm endplate.

The prosthesis used was a prototyp and had a constrained design with a ball and socket principle.

Results: Even the implantation of the lowest possible prosthesis height (5mm endplate) resulted in an increase of segmental lordosis (intact: 6.9; 5mm endplate: 8.8; p=0,027). Using a higher prosthesis (7mm endplate) further increased the segmental lordosis (10.5, p=0.041). The implantation of the lowest prosthesis resulted in significant increase of movement capability compared to the intact status for flexion-extension (8.6 vs 11.4; p=0.046) and axial rotation (2.9 vs 5.1; p=0.028). Lateral bending did not changed significantly (9.4 vs 8.6; p=0.345). The implantation of the higher prosthesis (7mm endplate) resulted in similar movement capability compared to intact status for flexion-extension (8.4 vs 8.6; p=0.116) and axial rotation (3.3 vs 2.9; p=0.600). Lateral bending decreased significantly compared to the intact status (5.1 vs 8.6; p=0.028).

Conclusion: Total disc replacement with the lowest prosthesis height inherently increases segmental lordosis. Further increase of disc height results in a significant enhancement of segmental lordosis by decreasing the range of motion for all three degrees of freedom. Yet, methods for scheduling the ideal disc height preoperatively, to provide a physiological lordosis thereby maintaining physiological range of motion postoperatively, seems not to be established already.